package integrity

import (
	"context"
	"fmt"
	"os"
	"path/filepath"
	"sync"
	"time"
)

// SimpleRecoveryHandler provides basic data recovery functionality
type SimpleRecoveryHandler struct {
	config          *IntegrityConfig
	backupDir       string
	recoveryStats   *RecoveryStats
	mu              sync.RWMutex
}

// NewSimpleRecoveryHandler creates a new simple recovery handler
func NewSimpleRecoveryHandler(config *IntegrityConfig, backupDir string) (*SimpleRecoveryHandler, error) {
	if config == nil {
		return nil, fmt.Errorf("config is required")
	}

	if backupDir == "" {
		return nil, fmt.Errorf("backup directory is required")
	}

	// Ensure backup directory exists
	if err := os.MkdirAll(backupDir, 0755); err != nil {
		return nil, fmt.Errorf("failed to create backup directory: %w", err)
	}

	handler := &SimpleRecoveryHandler{
		config:        config,
		backupDir:     backupDir,
		recoveryStats: &RecoveryStats{},
	}

	return handler, nil
}

// RecoverData attempts to recover corrupted data
func (r *SimpleRecoveryHandler) RecoverData(ctx context.Context, key string, metadata *IntegrityMetadata) ([]byte, error) {
	r.mu.Lock()
	r.recoveryStats.TotalAttempts++
	r.mu.Unlock()

	// Try different recovery methods in order
	recoveryMethods := []func(context.Context, string, *IntegrityMetadata) ([]byte, error){
		r.recoverFromBackup,
		r.recoverFromAlternateLocation,
		r.recoverUsingParity,
	}

	var lastErr error
	for _, method := range recoveryMethods {
		data, err := method(ctx, key, metadata)
		if err == nil {
			// Verify recovered data
			if err := r.verifyRecoveredData(data, metadata); err == nil {
				r.updateRecoveryStats(true)
				return data, nil
			}
		}
		lastErr = err
	}

	r.updateRecoveryStats(false)
	return nil, fmt.Errorf("all recovery methods failed: %w", lastErr)
}

// HasBackup checks if backup exists for given key
func (r *SimpleRecoveryHandler) HasBackup(ctx context.Context, key string) bool {
	backupPath := r.getBackupPath(key)
	_, err := os.Stat(backupPath)
	return err == nil
}

// CreateBackup creates backup for data
func (r *SimpleRecoveryHandler) CreateBackup(ctx context.Context, key string, data []byte) error {
	if !r.config.EnableBackup {
		return fmt.Errorf("backup is not enabled")
	}

	backupPath := r.getBackupPath(key)

	// Ensure backup directory exists
	backupDir := filepath.Dir(backupPath)
	if err := os.MkdirAll(backupDir, 0755); err != nil {
		return fmt.Errorf("failed to create backup directory: %w", err)
	}

	// Write backup atomically
	tempPath := backupPath + ".tmp"
	if err := os.WriteFile(tempPath, data, 0644); err != nil {
		return fmt.Errorf("failed to write backup: %w", err)
	}

	// Atomic rename
	if err := os.Rename(tempPath, backupPath); err != nil {
		os.Remove(tempPath) // Clean up temp file
		return fmt.Errorf("failed to create backup: %w", err)
	}

	return nil
}

// RestoreFromBackup restores data from backup
func (r *SimpleRecoveryHandler) RestoreFromBackup(ctx context.Context, key string) ([]byte, error) {
	backupPath := r.getBackupPath(key)

	data, err := os.ReadFile(backupPath)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, fmt.Errorf("backup not found for key %s", key)
		}
		return nil, fmt.Errorf("failed to read backup: %w", err)
	}

	return data, nil
}

// GetRecoveryStats returns recovery statistics
func (r *SimpleRecoveryHandler) GetRecoveryStats(ctx context.Context) (*RecoveryStats, error) {
	r.mu.RLock()
	defer r.mu.RUnlock()

	// Return a copy to avoid race conditions
	stats := *r.recoveryStats
	return &stats, nil
}

// Recovery methods

func (r *SimpleRecoveryHandler) recoverFromBackup(ctx context.Context, key string, metadata *IntegrityMetadata) ([]byte, error) {
	if !r.config.EnableBackup {
		return nil, fmt.Errorf("backup is not enabled")
	}

	if !r.HasBackup(ctx, key) {
		return nil, fmt.Errorf("no backup available for key %s", key)
	}

	return r.RestoreFromBackup(ctx, key)
}

func (r *SimpleRecoveryHandler) recoverFromAlternateLocation(ctx context.Context, key string, metadata *IntegrityMetadata) ([]byte, error) {
	// This is a placeholder for alternate location recovery
	// In a real implementation, this could check multiple storage locations,
	// replica nodes, or distributed storage systems
	return nil, fmt.Errorf("alternate location recovery not implemented")
}

func (r *SimpleRecoveryHandler) recoverUsingParity(ctx context.Context, key string, metadata *IntegrityMetadata) ([]byte, error) {
	// This is a placeholder for parity-based recovery
	// In a real implementation, this could use Reed-Solomon codes,
	// RAID-like parity information, or erasure coding
	return nil, fmt.Errorf("parity-based recovery not implemented")
}

func (r *SimpleRecoveryHandler) verifyRecoveredData(data []byte, metadata *IntegrityMetadata) error {
	if metadata == nil {
		return fmt.Errorf("no metadata provided for verification")
	}

	// Verify size
	if int64(len(data)) != metadata.Size {
		return fmt.Errorf("recovered data size mismatch: expected %d, got %d", metadata.Size, len(data))
	}

	// Verify hash
	calculator := NewHashCalculator(nil)
	if err := calculator.VerifyHash(context.Background(), data, metadata.Hash, metadata.Algorithm); err != nil {
		return fmt.Errorf("recovered data hash verification failed: %w", err)
	}

	// Verify checksum if available
	if len(metadata.Checksum) > 0 {
		checksumCalc := NewSimpleChecksumCalculator()
		if err := checksumCalc.VerifyChecksum(data, metadata.Checksum); err != nil {
			return fmt.Errorf("recovered data checksum verification failed: %w", err)
		}
	}

	return nil
}

func (r *SimpleRecoveryHandler) updateRecoveryStats(success bool) {
	r.mu.Lock()
	defer r.mu.Unlock()

	if success {
		r.recoveryStats.SuccessfulRecoveries++
	} else {
		r.recoveryStats.FailedRecoveries++
	}
	r.recoveryStats.LastRecoveryAt = time.Now()
}

func (r *SimpleRecoveryHandler) getBackupPath(key string) string {
	// Create a directory structure based on key hash to avoid too many files in one directory
	hash := fmt.Sprintf("%x", key) // Simple hash function
	if len(hash) < 4 {
		hash = "0000" + hash
	}

	dir1 := hash[:2]
	dir2 := hash[2:4]

	return filepath.Join(r.backupDir, dir1, dir2, key+".backup")
}

// AdvancedRecoveryHandler provides advanced recovery features
type AdvancedRecoveryHandler struct {
	*SimpleRecoveryHandler
	parityDir    string
	replicaNodes []string
}

// NewAdvancedRecoveryHandler creates a new advanced recovery handler
func NewAdvancedRecoveryHandler(config *IntegrityConfig, backupDir string, parityDir string, replicaNodes []string) (*AdvancedRecoveryHandler, error) {
	simpleHandler, err := NewSimpleRecoveryHandler(config, backupDir)
	if err != nil {
		return nil, err
	}

	if parityDir != "" {
		if err := os.MkdirAll(parityDir, 0755); err != nil {
			return nil, fmt.Errorf("failed to create parity directory: %w", err)
		}
	}

	return &AdvancedRecoveryHandler{
		SimpleRecoveryHandler: simpleHandler,
		parityDir:            parityDir,
		replicaNodes:         replicaNodes,
	}, nil
}

// CreateParityData creates parity data for redundancy
func (r *AdvancedRecoveryHandler) CreateParityData(ctx context.Context, key string, data []byte) error {
	if r.parityDir == "" {
		return fmt.Errorf("parity directory is not configured")
	}

	// This is a simplified implementation
	// In a real implementation, this would use Reed-Solomon codes or similar
	parityPath := filepath.Join(r.parityDir, key+".parity")

	// Simple XOR-based parity (for demonstration)
	parity := make([]byte, len(data))
	for i, b := range data {
		parity[i] = b ^ 0xFF // Simple XOR with 0xFF
	}

	if err := os.WriteFile(parityPath, parity, 0644); err != nil {
		return fmt.Errorf("failed to write parity data: %w", err)
	}

	return nil
}

// RecoverUsingParity recovers data using parity information
func (r *AdvancedRecoveryHandler) recoverUsingParity(ctx context.Context, key string, metadata *IntegrityMetadata) ([]byte, error) {
	if r.parityDir == "" {
		return nil, fmt.Errorf("parity directory is not configured")
	}

	parityPath := filepath.Join(r.parityDir, key+".parity")
	parityData, err := os.ReadFile(parityPath)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, fmt.Errorf("parity data not found for key %s", key)
		}
		return nil, fmt.Errorf("failed to read parity data: %w", err)
	}

	// Recover original data (reverse the XOR operation)
	recoveredData := make([]byte, len(parityData))
	for i, p := range parityData {
		recoveredData[i] = p ^ 0xFF
	}

	return recoveredData, nil
}

// ReconstructFromReplicas attempts to reconstruct data from replica nodes
func (r *AdvancedRecoveryHandler) ReconstructFromReplicas(ctx context.Context, key string) ([]byte, error) {
	if len(r.replicaNodes) == 0 {
		return nil, fmt.Errorf("no replica nodes configured")
	}

	// This is a placeholder for replica-based reconstruction
	// In a real implementation, this would:
	// 1. Contact replica nodes to get available data
	// 2. Use majority voting or similar consensus mechanism
	// 3. Reconstruct the original data

	return nil, fmt.Errorf("replica-based reconstruction not implemented")
}